Electrohydraulic steering controls are being developed for heavy-duty industrial machines because of their potential versatility over mechanical and hydraulic steering systems. Such electrohydraulic steering systems commonly use solenoid operated pilot valves for directing pilot fluid to a primary steering valve for steering the machine in response to manual manipulation of a steering control member, i.e. a steering wheel. The solenoid pilot valves are energized in response to electrical signals outputted from a sensor when the steering control member is moved in opposite directions from a neutral position. One of the concerns from a manufacturer's viewpoint is that customers are somewhat reluctant to purchase large machines in which the steering is dependent solely upon electrohydraulic circuitry.
In view of the above, it would be desirable to have an electrohydraulic steering system for the normal steering functions while having a simple mechanical/hydraulic steering arrangement interfaced therewith for steering the machine should a malfunction occur in the electrical circuitry.
The present invention is directed to overcoming one or more of the problems as set forth above.